The present invention relates to polyorganosiloxane compositions that may be used to treat the surface of substrates such as papers, rubbers, plastics and metals to impart non-sticking, water-repelling, abrasion-resistant, sliding and luster-preventing properties. The present invention further relates to polyorganosiloxane compositions that may be used to form a primer film which improves the adhesive ability of other polysiloxane compositions when they are applied onto a substrate.
Heretofore, various types of polyorganosiloxane compositions have been employed in the treatment of the surface of substrates in order to impart to it a non-sticking property.
The prior art compositions may be classified as follows:
(1) Solutions prepared by adding a polyorganosiloxane containing Si--H bonds and/or an organoalkoxysilane to a polydiorganosiloxane terminated by hydroxy groups, and further admixing an organic tin compound and an organic solvent;
(2) Aqueous emulsions prepared by adding a polyorganosiloxane containing Si--H bonds and/or an organoalkoxysilane to a polydiorganosiloxane terminated by hydroxy groups, further admixing a polyvinylalcohol, followed by emulsification with water;
(3) Compositions comprising a polyorganosiloxane containing two or more vinyl groups in the molecule, a polyorganosiloxane containing Si--H bond, a platinum or a platinum compound, an organic solvent and/or a curing-inhibitor.
These polyorganosiloxane compositions have an excellent property of affording non-sticking film onto the surface of substrates. However, they involve a disadvantage in that a cured silicone layer tends to slip off a rubber or plastic substrate. Further, in the case of compositions (3) mentioned above where they are used for the surface-treatment of such substrates as natural rubbers, ordinary synthetic rubbers or soft polyvinyl chlorides, the platinum or the platinum compound contained in the compositions (3) tends to be deactivated by the vulcanizing agent, vulcanization-accelerater or plasticizer contained in the substrates, whereby curing of the compositions (3) tends to be prevented.
The present inventors earnestly studied the disadvantages mentioned above and attempted to impart to the surface of substrates, in particular rubbers and plastics, excellent non-sticking, water-repelling and abrasion-resistant properties. As a result, it was found that the sliding property could be imparted to cured films by use of a composition comprising (a) a polyorganosiloxane having at least two monovalent hydrocarbyl groups substituted by an epoxy-containing group (such as a glycidoxy group and/or an epoxycyclohexyl group) bonded to a silicon atom in the molecule, and (b) a silane and/or siloxane having a substituted or unsubstituted amino group bonded to a silicon atom via at least one carbon atom and having one or more alkoxy groups bonded to a silicon atom, and (c) a polydiorganosiloxane having terminated by hydroxyl groups, whereby the polydiorganosiloxane participates in the formation of the network structure by means of an alcohol-eliminating condensation reaction between the alkoxy groups of the silane and/or siloxane having such alkoxy groups, and the polydiorganosiloxane. It was also found that, by adding a polyorganohydrogensiloxane and a metal salt of a fatty acid to the compositions mentioned above, and by allowing a hydrogen-eliminating condensation reaction to take place simultaneously between the polyorganosiloxane terminated by a hydroxy group and the polyorganohydrogensiloxane, the curing rate upon heat-curing could be promoted (Japanese Provisional Patent Publication No. 79-45361).
However, the sliding property of the rubber surface against glass or coated steel plate was not sufficient. Further, since luster appeared by treatment of the surface, this method was unsuitable where luster should be avoided.
In order to cope with this, there may be further admixed a powder such as aerosol silica. However, addition of a small amount thereof is not sufficient to diminish luster, whereas addition of an increased amount thereof has made it difficult to attain a uniform mixture. Similarly, there may be included a fluorocarbon resin powder. However, also in this case, a sufficient amount to diminish luster could not be obtained. Moreover, a large quantity of a fluorocarbon resin powder is required in order to attain the desired sliding property. Further, there is a problem in that this method brings about a white powdery appearance of the surface thus treated, which is not a desired result.